PostgreSQL? Isn't that an open-source database? It can handle that load?

Indeed.

Hi5 runs hundreds of PostgreSQL servers in one of the world's largest commercial OLTP PostgreSQL installations. All Hi5 subscriber data, including user profiles, metadata associated with user photos, and comments, is stored on the company's PostgreSQL databases...In June 2008, the PostgreSQL-based system delivered more than 18.5 billion page views, serving nearly 11 million visitors to the site every day.

A key challenge and requirement for Hi5 is that the social-networking site cannot be taken offline for maintenance. The company's PostgreSQL databases must deliver exceptional stability and performance 24 hours per day, seven days per week, 365 days per year to serve users around the globe. Any issues must be resolved in real time, with the system still running.

However, the real story in Hi5's decision is its work with EnterpriseDB. The Web 2.0 world has traditionally adopted open source heavily...and paid little to nothing for it. Hence, the real news here is one Web 2.0 company's realization that buying support for open-source software makes a lot of sense/cents.

In Hi5's case, it was already using PostgreSQL before it selected EnterpriseDB to offer services around its PostgreSQL deployment. EnterpriseDB did a quick review with Hi5, discovered that its PostgreSQL deployment wasn't optimized, and convinced Hi5 that it could improve PostgreSQL's performance.

The rest is history. Hi5 is now getting better performance on its PostgreSQL deployment and using less hardware. Sure, it's paying EnterpriseDB for the service, but saving money in the process.

Yes, there are likely some Web 2.0 outfits that really can scale MySQL, PostgreSQL, Linux, etc. as well as anyone can, but guess what? They're probably not you. Most companies could use some help: support, consulting, training, etc. Save while you spend. It's really not complicated.